It is important to control tension in a thread as it is being fed into a knitting or fabric weaving machine. Preferably, thread tension should remain constant during such feeding process. This is important because as is well-known in the art, nonuniform thread tension adversely affects the knit or weave of the fabric. A number of devices and method have been developed for controlling thread tension, and have been disclosed in the following United States Patents: U.S. Pat. No. 3,014,356 issued to Butler on Dec. 26, 1961; U.S. Pat. No. 3,188,713 issued to Dyer on June 15, 1965; U.S. Pat. No. 3,364,889 issued to Wiener on Jan. 23, 1968; U.S. Pat. No. 3,994,166 issued to Hermanns on Mar. 16, 1976; U.S. Pat. No. 4,119,253 issued to Benson on Oct. 10, 1978; and U.S. Pat. No. 4,297,834 issued to Franzen on Nov. 3, 1981.
The above-cited patents generally teach the use of an airflow to control the advancement of thread, or to control thread tension. Several of these patents, and specifically, Butler, Wiener, Hermanns and Benson teach using an airflow to control thread tension, wherein the thread is fed and advanced through a passageway and an airflow traveling through the passageway in an opposing direction causes tension in the thread. The present invention utilizes this general concept. These patents, however, introduce the airflow into the passageway in a manner that is different from the instant invention.
Referring now to FIG. 10, which schematically illustrates the teachings of several of the above patents, therein is shown a hollow cylindrical tube 1 that provides a passageway for thread advancement. The thread would advance through the tube 1 in the direction indicated by arrow 2. Air is fed from a chamber 3 by means of an orifice 4 into the tube 1. Air is fed into the chamber 3 from an air supply means, wherein the air is fed into the side of the chamber 3 from a tube 5. It is to be understood, of course, that FIG. 10 is merely a schematic drawing and is provided herein for the purpose of demonstrating at least some of the differences between the prior art and the present invention.
A problem with using an airflow to control thread tension in the manner shown in FIG. 10 is that by introducing an airflow from the side tube 5, a swirling airflow is generated in the chamber 3. Such swirling or turbulent airflow is then communicated onward into tube 1 in the manner shown by arrows 6. This places a twist on the thread as it travels through the tube 1. Another problem is that the amount of airflow from chamber 3 into the tube 1 is governed not by adjusting the orifice 4, but by adjusting the amount of airflow that is fed into the chamber 3 from the side tube 5.
Referring now to FIG. 11, therein is shown a schematic representation showing at least one difference between the present invention and the prior art. The present invention provides an airflow 7 that travels in substantially the same direction as the direction of thread advancement 2. The airflow 7 is reversed and directed by an orifice 8 into the inner passageway, formed by hollow tube 1, wherein the airflow then opposes the advancement of the thread. By supplying the airflow into the tube 1 in this manner, the airflow is introduced into the tube in a smooth and nonturbulent manner, wherein the airflow streamlines are parallel to the direction of thread advancement.
It should be appreciated that Franzen, U.S. Pat. No. 4,297,834, teaches a similar reversal of airflow as that which is shown in FIG. 11. There are, however, differences between Franzen and the present invention which make the present invention patentable over Franzen. One major difference is that in Franzen an airflow is directed downwardly along a passageway 21, wherein the airflow is not used to control tension in the thread. The airflow in the passageway 21 travels in the same direction as the thread advancement. In the instant invention, and in the other prior art references cited above, the airflow is used to oppose thread advancement. The airflow created in the passageway 21 of Franzen is created for the purpose of causing a vacuum that pulls a yarn braking body 7 downwardly. The Franzen device controls thread tension by utilizing a braking body 7 and a braking surface 4. Pulling the braking body 7 away from the braking surface 4 permits thread advancement. This is undesirable because the thread is constantly in sliding contact with a surface.
The present invention addresses the known problems associated with the prior art, and others.